Interventional or surgical procedures are necessary in order to carry out numerous medical examinations. Such procedures are performed with the aid of X-ray systems. Thus, radiological interventions are frequently carried out for the purpose of diagnosing or treating vascular diseases, such interventions involving guiding an instrument, in particular a catheter, through a peripheral blood vessel to the point of interest in the body with the aid of X-ray fluoroscopy. Controlling an instrument of this kind can sometimes be very demanding, in particular if the blood vessels are very convoluted and have many branches. In order to improve navigation for the examining physician, an intervention of this kind is typically monitored by means of a monoplane or biplane imaging X-ray system. In this process the position of the instruments, such as, for example, catheters, guide wires or stents, can be captured very accurately in the X-ray images displayed during the intervention. However, in two-dimensional fluoroscopy images of this kind the three-dimensional anatomy of the patient can be recognized only to an inadequate degree. In certain interventional procedures, such as in neuroradiology, for example, and in electrophysiological examinations it is very difficult for the physician to find his or her bearings in the three-dimensional anatomy of the patient on the basis of the two-dimensional fluoroscopy images.
In order to improve orientation and therefore navigation it is known to record three-dimensional images of the area under examination prior to the intervention by means of a 3D imaging modality and display them during the intervention overlaid with the 2D fluoroscopy images. The three-dimensional images can be recorded prior to the examination using, for example, a magnetic resonance (MR), a computer tomography (CT), a positron emission tomography (PET) or a 3D ultrasound system. 3D angiography images can also be recorded in advance using the same angiography system by means of which the X-ray fluoroscopy images are also generated. The geometrical relationship between the image data sets must be known in any case for the subsequent 2D/3D overlaying of the images. This can be achieved either by calibration or by 2D/3D registration of the image data. Thus, for example, DE 102 10 646 A1 discloses a method of visualizing a medical instrument that has been introduced into an area of examination inside a patient, wherein the respective current position of the instrument in a three-dimensional environment is recognizable on a monitor by means of a 2D/3D registration and overlay of the aforementioned kind.